Electric toothbrush

ABSTRACT

An electric toothbrush is provided with a brush portion, a motor including a rotary shaft, a battery, which supplies the motor with power supply voltage, and an eccentric shaft, which rotates together with the rotary shaft. The eccentric shaft has a center of gravity located at a position deviated from an axis of the rotary shaft of the motor. An oscillation transmission mechanism transmits oscillations generated by the rotation of the eccentric shaft. An oscillation amplitude regulation circuit regulates an oscillation amplitude of the brush portion to be constant regardless of changes in the power supply voltage in a state in which the brush portion is free from external loads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2008-168727, filed on Jun. 27, 2008, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an electric toothbrush.

A typical electric brush includes a brush portion that is oscillated bya motor. Japanese Laid-Open Patent Publication No. 9-173360 describes anelectric toothbrush including a motion conversion mechanism, whichconverts the rotation produced by a motor to two types of differentmotions that are transmitted to the brush portion so as to move thebrush portion in constant oscillation amplitude. Japanese Laid-OpenPatent Publication No. 2008-80099 describes an electric toothbrushincluding an eccentric shaft, which generates oscillations when rotatedby a motor, and an oscillation transmission component, which transmitsthe oscillation of the eccentric shaft to the brush portion, so as toreduce power consumption and produce high-speed rotations.

SUMMARY OF THE INVENTION

In the electric toothbrush of the '360 publication, the motionconversion mechanism mechanically converts the rotation of the motor tooscillation of the brush portion so as to oscillate the brush portion inconstant oscillation amplitude. However, due to the external loadapplied by the brush portion, it is difficult for the motor to producehigh-speed rotations. Further, this electric toothbrush consumes muchpower.

In the electric toothbrush of the '099 electric toothbrush, theeccentric shaft is rotated to generate oscillations so as to producehigh-speed rotations. However, as the power supply voltage decreases,the oscillation amplitude of the brush portion decreases and lowers thebrushing performance.

It is an object of the present invention to provide an electrictoothbrush that produces high-speed rotations with a motor and alwaysmoves the brush portion in constant oscillation amplitude even when thepower supply voltage decreases.

One aspect of the present invention is an electric toothbrush providedwith a brush portion, a motor including a rotary shaft, a battery whichsupplies the motor with power supply voltage, and an eccentric shaftwhich rotates together with the rotary shaft. The eccentric shaft has acenter of gravity located at a position deviated from an axis of therotary shaft of the motor. An oscillation transmission mechanismtransmits oscillations generated by the rotation of the eccentric shaftto the brush portion. An oscillation amplitude regulation circuitregulates an oscillation amplitude of the brush portion to be constantregardless of changes in the power supply voltage in a state in whichthe brush portion is free from external loads.

Other aspects and advantages of the present invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1( a) is a cross-sectional side view and FIG. 1( b) is across-sectional plan view, each showing a first embodiment of anelectric toothbrush;

FIG. 2 is a block diagram of the electric toothbrush shown in FIG. 1;

FIG. 3 is a graph showing the relationship between the oscillationamplitude of a brush portion, the power supply voltage, and the rotationspeed of a motor;

FIGS. 4( a) to 4(c) are timing charts showing the relationship betweenthe time power supply voltage is supplied and the rotation speed of themotor;

FIG. 5 is a block diagram of a second embodiment of an electrictoothbrush;

FIG. 6 is a block diagram of a third embodiment of an electrictoothbrush; and

FIG. 7 is a block diagram of a fourth embodiment of an electrictoothbrush.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of an electric toothbrush according to the presentinvention will now be discussed.

Referring to FIG. 1, an electric toothbrush 10 includes a grip, or case11, and a brush unit 12, which is detachably attached to the distal endof the case 11. The case 11 may be elongated and cylindrical. The case11 accommodates a motor 13 and a battery 20, which supplies power supplyvoltage. A switch button 14 arranged on the case 11 is used to switchthe motor 13 ON and OFF.

The motor 13 includes a rotary shaft 13 a, which extends toward thedistal end of the case 11 in the longitudinal direction of the case 11.An eccentric shaft 15 is attached to the rotary shaft 13 a. Theeccentric shaft 15 includes an elongated main shaft body 15 a and aweight 15 b, the center of gravity of which is deviated in the radialdirection from the axis of the rotary shaft 13 a. The weight 15 b isattached to the distal end of the main shaft body 15 a.

The eccentric shaft 15 is enclosed in an oscillation transmission member16, which functions as an oscillation transmission mechanism. Theoscillation transmission member 16 is fixed to the case 11 via avibration suppression member, or resilient damper 17. The eccentricshaft 15 has a distal end rotatably supported by a bearing 16 a formedin the oscillation transmission member 16. Rotation of the eccentricshaft 15 oscillates the oscillation transmission member 16 relative tothe case 11.

The oscillation transmission member 16 is enclosed in the brush unit 12.The brush unit 12 includes a tube 18, in which the oscillationtransmission member 16 is arranged, and a brush portion 19, which isfixed to the distal end of the tube 18. The brush unit 12 is aconsumable product and detachable from the oscillation transmissionmember 16 to enable replacement. Oscillation of the oscillationtransmission member 16 oscillates the brush portion 19. A user holds thecase 11, switches the power ON, and brushes his or her teeth with theoscillating brush portion 19 to clean the teeth. The oscillationamplitude S of the brush portion 19 is shown by the double-headed arrowin FIG. 1( b).

An electrical circuit for oscillating the brush unit 12 will now bediscussed.

As shown in FIG. 2, the motor 13 is connected to a transistor 21, whichserves as a switch element. A terminal of the motor 13 may be connectedto the positive terminal of a battery 20 and another terminal of themotor 13 may be connected to the collector terminal of the transistor21. The emitter terminal of the transistor 21 is connected to thenegative terminal of the battery 20. Thus, the motor 13 is connected inseries with the battery 20 via the transistor 21. When the base terminalof the transistor 21 is provided with a voltage signal (flow ofcurrent), the motor 13 is supplied with power supply voltage from thebattery 20.

The battery 20 is connected to a power supply circuit 22. The powersupply circuit 22 may include a booster circuit, which increases thepower supply voltage from the battery 20. Further, the power supplycircuit 22 is connected to a control unit 23, which functions as anoscillation amplitude regulation circuit. The control unit 23 detectsthe power supply voltage supplied to the motor 13 from the battery 20.

The control unit 23 is connected to the base terminal of the transistor21. Based on the value of the detected power supply voltage from thebattery 20, the control unit provides the base terminal with apredetermined voltage signal to switch ON and OFF the transistor 21(duty-control). That is, the control unit 23 outputs a voltage signalover pulse duration periods that are based on the value of the detectedpower supply voltage from the battery 20. This supplies the motor 13with the power supply voltage from the battery 20 in pulses of a pulseduration period that is based on the value of the power supply voltageand thereby produces rotation with the motor 13. Such a process will nowbe discussed in further detail.

Referring to FIG. 3, the oscillation amplitude S of the brush portion 19usually decreases as the power supply voltage supplied to the motor 13increases, and the oscillation amplitude S increases as the power supplyvoltage decreases. Further, the rotation speed of the motor 13 usuallyincreases as the power supply voltage supplied to the motor 13increases, and the rotation speed of the motor 13 decreases as the powersupply voltage supplied to the motor 13 decreases. Factors such as thelength and diameter of the eccentric shaft 15 and the heaviness of theweight 15 b vary the relationship between the power supply voltagesupplied to the motor 13 and the rotation speed of the motor 13. Forexample, the rotation speed of the motor 13 may decrease as the powersupply voltage increases. In other situation, the rotation speed of themotor 13 may reach a peak when the power supply voltage is intermediate.It is thus apparent that the oscillation amplitude S of the brushportion 19 varies as the rotation speed of the motor 13 varies. In thefirst embodiment, the oscillation amplitude S of the brush portion 19decreases as the rotation speed of the motor 13 increases.

Based on the value of the detected power supply voltage from the battery20, the control unit 23 provides the base terminal of the transistor 21with pulses of a voltage signal (pulse signal), which is generated tokeep the rotation speed of the motor 13 constant. For example, when thevalue of the detected power supply voltage from the battery 20increases, the control unit 23 shortens the pulse duration period duringwhich the voltage signal is provided. When the value of the detectedpower supply voltage from the battery 20 decreases, the control unit 23lengthens the pulse duration period during which the voltage signal isprovided.

In one example, pulse duration periods set to keep the rotation speed ofthe motor 13 constant based on the value of the power supply voltagefrom the battery 20 are stored beforehand in a memory of the controlunit 23. A pulse duration period PD is illustrated in FIG. 4( a). Thecontrol unit 23 provides the base terminal with a voltage signal over apulse duration period corresponding to the value of the detected powersupply voltage from the battery 20.

The motor 13 applies drive force to the rotary shaft 13 a over the pulseduration periods during which it is supplied with power supply voltage.The interval is extremely short between the pulse duration periodsduring which power supply voltage is supplied. Thus, fluctuations in therotation produced by the motor 13 are subtle and ignorable, and therotation may be approximated as rotation at a constant speed. When thepulse duration periods during which the power supply voltage is suppliedare relatively short as shown in FIG. 4( a), the constant speed may beslightly lower than when the motor 13 is continuously supplied with thepower supply voltage.

In the first embodiment, the control unit 23 function to shorten thepulse duration period Pd during which the motor 13 is supplied withpower supply voltage (refer to FIG. 4( a)) as the power supply voltagefrom the battery increases and lengthen the pulse duration period Pdduring which the motor 13 is supplied with power supply voltage as thepower supply voltage from the battery decreases. This regulates themotor 13 to a constant rotation speed. In this manner, the oscillationamplitude S of the brush portion 19 is regulated to be constant. In thefirst embodiment, the control unit 23 and the transistor 21 function asa pulse generation circuit.

FIG. 4 shows the power supply voltage, which is supplied in pulses, andthe rotation speed of the motor 13. FIGS. 4( a), 4(b), and 4(c) showsituations in which the state of charge of the battery (batterycapacitance or remaining battery level) are respectively high,intermediate, and low, for example, 100%, 50%, and about 0%. The powersupply voltage of the battery 20 in the first embodiment is related tothe state of charge of the battery 20.

The control unit 23, which is connected to the switch button 14, startsthe motor 13 when the switch button 14 is switched ON. The battery 20may be connected to a charging circuit 24. In such a case, the chargingcircuit 24 charges the battery 20 when the charging circuit 24 isconnected to an external power supply.

The first embodiment has the advantages described below.

(1) The oscillation amplitude regulation circuit detects the value ofthe power supply voltage supplied from the battery 20 and supplies themotor 13 with the power supply voltage in pulses of a pulse durationperiod set in accordance with the value of the power supply voltage. Inone example, the oscillation amplitude regulation circuit regulates therotation speed of the motor 13 to be constant by shortening the pulseduration period during which the power supply voltage is supplied whenthe value of the detected power supply voltage increases, andlengthening the pulse duration period during which the power supplyvoltage is supplied when the value of the detected power supply voltagedecreases. Thus, the oscillation amplitude regulation circuit regulatesthe oscillation amplitude S of the brush portion 19 to keep it constantregardless of changes in the power supply voltage of the battery 20.This allows for the oscillation amplitude regulation circuit to producehigh-speed rotations with the motor 13, while regulating the oscillationamplitude S of the brush portion 19 to always be constant even when thepower supply voltage decreases. Thus, even when used for a long time,the brushing performance of the electric toothbrush 10 is not lowered.

A second embodiment of the present invention will now be discussed. Likeor same reference numerals are given to those components that are thesame as the corresponding components of the first embodiment. Suchcomponents will not be described below.

Referring to FIG. 5, the battery 20 is connected via the switch button14 to a constant voltage circuit 31, which functions as an oscillationamplitude regulation circuit. When the switch button 14 is switched ON,the constant voltage circuit 31 is supplied with power supply voltagefrom the battery 20. When the switch button 14 is switched OFF, thesupply of power supply voltage to the constant voltage circuit 31 isstopped (cut).

The constant voltage circuit 31 is connected to the motor 13. Theconstant voltage circuit 31 converts the power supply voltage suppliedfrom the battery 20 into a predetermined constant voltage and suppliesthe motor 13 with the constant voltage. The constant voltage suppliedfrom the constant voltage circuit 31 rotates the rotary shaft 13 a ofthe motor 13.

In the second embodiment, the constant voltage circuit 31 converts thepower supply voltage to voltage C (constant voltage), which is shown inFIG. 3. The voltage C is predetermined as a value that is lower than themaximum value A of the power supply voltage and drives the motor 13 at arotation speed that is high and satisfactory. This allows for the motor13 to produce high-speed rotations. When the value of the power supplyvoltage supplied from the battery 20 is higher than the voltage C, theconstant voltage circuit 31 converts (lowers) the power supply voltageto the voltage C. When the value of the power supply voltage suppliedfrom the battery 20 decreases to the voltage C or lower, the constantvoltage circuit 31 converts (increases) the power supply voltage to thevoltage C. This regulates the oscillation amplitude S of the brushportion 19 to be constant regardless of the decrease in the power supplyvoltage of the battery 20.

The second embodiment has the same advantages as the first embodiment.

A third embodiment of the present invention will now be discussed.

Referring to FIG. 6, the motor 13 has one terminal connected to thepositive terminal of the battery 20 and another terminal connected tothe collector terminal of the transistor 21. The emitter terminal of thetransistor 21 is connected to the negative terminal of the battery 20.

The battery 20 is connected to the power supply circuit 22. The powersupply circuit 22 is connected to the control unit 23, which includes aCPU and a RAM. The power supply circuit 22 supplies the control unit 23with drive voltage that is suitable for driving the control unit 23. Thecontrol unit 23 is connected to the battery 20 and detects the powersupply voltage supplied from the battery 20 to the motor 13. A rotationspeed detection circuit 41 is connected to the control unit 23 to detectthe rotation speed of the motor 13. This allows for the control unit 23to detect the rotation speed of the motor 13.

Based on both the value of the detected power supply voltage from thebattery 20 and the rotation speed of the motor 13, the control unit 23provides the base terminal of the transistor 21 with a predeterminedvoltage signal to switch ON and OFF the transistor 21. This will now bedescribed in further detail.

The control unit 23 provides the base terminal of the transistor 21 witha voltage signal over a pulse duration period that is in accordance withboth the value of the detected power supply voltage from the battery 20and the rotation speed of the motor 13. This supplies the motor 13 withthe power supply voltage from the battery 20 in pulses of a pulseduration period that is in accordance with both the value of thedetected power supply voltage from the battery 20 and the rotation speedof the motor 13 and thereby produces rotation with the motor 13.

In one example, pulse duration periods set to keep the rotation speed ofthe motor 13 constant in accordance with both the value of the detectedpower supply voltage from the battery 20 and the rotation speed of themotor 13 are stored beforehand in a memory of the control unit 23. Thecontrol unit 23 provides the base terminal with a voltage signal over apulse duration period corresponding to both the value of the detectedpower supply voltage from the battery 20 and the rotation speed of themotor 13. This supplies the motor 13 with the power supply voltage fromthe battery 20 in pulses. The motor 13 applies a drive force to therotary shaft 13 a over the pulse duration period during which it issupplied with power supply voltage. The interval is extremely shortbetween the pulse duration periods during which power supply voltage issupplied. Thus, fluctuations in the rotation produced by the motor 13are subtle and ignorable, and the rotation may be approximated asrotation at a constant speed.

In the third embodiment, the control unit 23 shortens the pulse durationperiod during which the motor 13 is driven when the value of the powersupply voltage from the battery 20 is high. Further, the control unit 23lengthens the pulse duration period during which the motor 13 is drivenwhen the value of the power supply voltage from the battery 20 is low.When the rotation speed of the motor 13 becomes lower than apredetermined rotation speed, the control unit 23 lengthens (prolongs)the pulse duration period during which the motor 13 is driven. Thisregulates the rotation speed of the motor 13 to be constant even whenthe power supply voltage of the battery 20 decreases or when an externalload applied to the brush portion 19 impedes the rotation of the rotaryshaft 13 a. As a result, the oscillation amplitude S of the brushportion 19 is regulated to be constant.

As discussed above in detail, in addition to the advantages of the firstembodiment, the third embodiment has the advantages described below.

(2) The oscillation amplitude regulation circuit supplies the motor 13with the power supply voltage in pulses of a pulse duration period setin accordance with the value of the power supply voltage from thebattery 20 and the rotation speed of the motor 13 detected by therotation speed detection circuit 41. Thus, the brush portion 19 alwayscontinuously moves in constant oscillation amplitude even when theexternal load applied to the brush portion 19 lowers the rotation speedof the motor 13. This prevents the brushing performance of the electrictoothbrush 10 from being lowered during use. Further, the power supplyvoltage of the battery 20 is used without undergoing any conversions.This suppresses unnecessary drainage of the battery 20 and prolongs thelife of the battery 20.

A fourth embodiment of the present invention will now be discussed.

Referring to FIG. 7, the motor 13 has one terminal connected to thepositive terminal of the battery 20 and another terminal connected tothe collector terminal of the transistor 21. The emitter terminal of thetransistor 21 is connected to the negative terminal of the battery 20.

The battery 20 is connected to the power supply circuit 22. The powersupply circuit 22 is connected to the control unit 23, which functionsas the oscillation amplitude regulation circuit. The control unit 23includes a CPU and a RAM. The power supply circuit 22 supplies thecontrol unit 23 with drive voltage that is suitable for driving thecontrol unit 23. The control unit 23 is connected to the battery 20 anddetects the power supply voltage supplied from the battery 20 to themotor 13. A load current detection circuit 51 is connected to thecontrol unit 23 to detect the current flowing to the motor 13. Thisallows for the control unit 23 to detect the load current of the motor13.

Based on both the value of the detected power supply voltage from thebattery 20 and the load current of the motor 13, the control unit 23provides the base terminal of the transistor 21 with a predeterminedvoltage signal to switch ON and OFF the transistor 21. This will now bedescribed in further detail.

Duration periods set to keep the rotation speed of the motor 13 constantin accordance with both the value of the power supply voltage from thebattery 20 and the load current of the motor 13 are stored beforehand ina memory of the control unit 23. The control unit 23 provides the baseterminal with a voltage signal over a pulse duration periodcorresponding to both the value of the detected power supply voltagefrom the battery 20 and the load current of the motor 13. This suppliesthe motor 13 with the power supply voltage from the battery 20 inpulses. The motor 13 applies a drive force to the rotary shaft 13 a overthe pulse duration periods during which it is supplied with power supplyvoltage. The interval is extremely short between the pulse durationperiods during which power supply voltage is supplied. Thus,fluctuations in the rotation produced by the motor 13 are subtle andignorable, and the rotation may be approximated as rotation at aconstant speed.

In the fourth embodiment, the control unit 23 shortens the pulseduration periods during which the motor 13 is driven when the value ofthe power supply voltage from the battery 20 is high. Further, thecontrol unit 23 lengthens the pulse duration periods during which themotor 13 is driven when the power supply voltage is low. Extensions areset beforehand for the pulse duration periods during which the motor 13is driven in accordance with the load current of the motor 13 andstored, for example, the memory of the control unit 23. This regulatesthe rotation speed of the motor 13 to be constant even when the powersupply voltage of the battery 20 decreases or when an external loadapplied to the brush portion 19 impedes the rotation of the rotary shaft13 a. As a result, the oscillation amplitude S of the brush portion 19is regulated to be constant.

As discussed above in detail, in addition to the advantages of the firstembodiment, the fourth embodiment has the advantages described below.

(3) The oscillation amplitude regulation circuit detects the value ofthe power supply voltage supplied from the battery 20 and supplies themotor 13 with the power supply voltage in pulses of a pulse durationperiod set beforehand in accordance with the load current of the motor13 detected by the load current detection circuit 51. Thus, the brushportion 19 always continuously moves in constant oscillation amplitudeeven when external load is applied to the brush portion 19. Thisprevents the brushing performance of the electric toothbrush 10 frombeing lowered during use. Further, the power supply voltage of thebattery 20 is used without undergoing any conversions. This suppressesunnecessary drainage of the battery 20 and prolongs the life of thebattery 20.

It should be apparent to those skilled in the art that the presentinvention may be embodied in many other specific forms without departingfrom the spirit or scope of the invention. Particularly, it should beunderstood that the present invention may be embodied in the followingforms.

In the second and third embodiments, the oscillation amplituderegulation circuit detects the rotation speed or load current of themotor 13, measures the external load applied to the motor 13, and varies(prolongs) the pulse duration periods during which power supply voltageis supplied in accordance with the measured external load. Instead ofthe rotation speed or load current, the oscillation amplitude regulationcircuit detects back electromotive force. More specifically, if aexternal load is produced, the oscillation amplitude regulation circuitmay detect the back electromotive force generated when the motor 13 isnot supplied with power supply voltage, measure the external loadapplied to the motor 13, and vary (prolong) the pulse duration periodsduring which power supply voltage is supplied in accordance with thevalue of the measured back electromotive force.

The present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

1. An electric toothbrush comprising: a brush portion; a motor includinga rotary shaft; a battery which supplies the motor with power supplyvoltage; an eccentric shaft which rotates together with the rotaryshaft, in which the eccentric shaft has a center of gravity located at aposition deviated from an axis of the rotary shaft of the motor; anoscillation transmission mechanism which transmits oscillationsgenerated by the rotation of the eccentric shaft to the brush portion;and an oscillation amplitude regulation circuit which regulates anoscillation amplitude of the brush portion to be constant regardless ofchanges in the power supply voltage in a state in which the brushportion is free from external loads.
 2. The electric toothbrushaccording to claim 1, wherein the oscillation amplitude regulationcircuit includes a pulse generation circuit which supplies the motorwith the power supply voltage in pulses of a predetermined pulseduration period set to regulate the oscillation amplitude of the brushportion to be constant in accordance with the value of the power supplyvoltage supplied from the battery.
 3. The electric toothbrush accordingto claim 1, wherein the oscillation amplitude regulation circuitconverts the power supply voltage supplied from the battery intoconstant voltage for regulating the oscillation amplitude of the brushportion to be constant, and supplies the motor with the constantvoltage.
 4. The electric toothbrush according to claim 2, wherein theoscillation amplitude regulation circuit: detects load current appliedto the motor when external load is applied to the motor; and suppliesthe motor with the power supply voltage in pulses of the predeterminedpulse duration period set to regulate the oscillation amplitude of thebrush portion to be constant in accordance with both the value of thepower supply voltage supplied from the battery and the value of thedetected load current.
 5. The electric toothbrush according to claim 2,wherein the oscillation amplitude regulation circuit: detects rotationspeed of the motor when external load is applied to the motor; andsupplies the motor with the power supply voltage in pulses of thepredetermined pulse duration period set to regulate the oscillationamplitude of the brush portion to be constant in accordance with boththe value of the power supply voltage supplied from the battery and thedetected rotation speed.
 6. The electric toothbrush according to claim2, wherein the oscillation amplitude regulation circuit: detects backelectromotive force of the motor when external load is applied to themotor; and supplies the motor with the power supply voltage in pulses ofthe predetermined pulse duration period set to regulate the oscillationamplitude of the brush portion to be constant in accordance with boththe value of the power supply voltage supplied from the battery and thevalue of the detected electromotive force.
 7. The electric toothbrushaccording to claim 2, wherein the pulse generation circuit includes: amemory which stores the value of the power supply voltage supplied fromthe battery in association with the predetermined pulse duration periodset to regulate the oscillation amplitude of the brush portion to beconstant; and a switch element which functions in accordance with apulse signal having a pulse duration period stored in the memory;wherein the power supply voltage is supplied in pulses to the motor viathe switch element.